Tail for Balance

 In the more distant past, we are thinking about 100 years ago possibly, Megatherium was not considered a bipedal animal. It may have been described as facultatively bipedal, meaning it could occasionally walk on two feet, at most. The most often that Megatherium was thought to have engaged in such behavior was during its feeding forays. It was also hypothesized, in the past, that the tail was used as peg upon which Megatherium could balance its weight while foraging in trees on two legs. This impression was captured in the restoration of Robert Bruce Horsfall published in 1913. This tripod of legs and tail remains relatively popular. However, Casinos (1996) did conduct biomechanical analyses that suggested that the vertebral column and the femur were constructed and situated such that they would resist bending that they would be subjected to if Megatherium was an obligate quadruped, that is, if they were only able to walk on four legs. The analyses appear to indicate that Megatherium was adapted to a bipedal lifestyle and that the strong muscular tail, while it may have acted as an element in a tripod feeding stance, was not only strong and robust to resist this tripod feeding stance.

Literature Cited

Casinos, A. (1996). "Bipedalism and quadrupedalism in Megatherium: An attempt at biomechanical reconstruction". Lethaia. 29: 87–96. doi:10.1111/j.1502-3931.1996.tb01842.x.